Midamble allocations for MIMO transmissions

ABSTRACT

Allocation of multiple training sequences transmitted in a MIMO timeslot from multiple transmit antenna elements is provided. For example, a method of generating signals in a MIMO timeslot, the method comprising: selecting a first training sequence; preparing a first data payload; generating a first signal including the prepared first data payload and the first training sequence; transmitting the first signal in a MIMO timeslot from a first antenna of a network element; selecting a second training sequence, wherein the second training sequence is different from first training sequence; preparing a second data payload; generating a second signal including the prepared second data payload and the second training sequence; and transmitting the second signal in the MIMO timeslot from a second antenna of the network element.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present continuation application claims the benefit of priorityunder 35 U.S.C. 120 to application Ser. No. 11/122,387, filed May 4,2005, which claims the benefit of U.S. Provisional Application Ser. No.60/568,194, filed May 4, 2004, the disclosure of both of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to demodulation of radio signals from atransmitter having collocated transmit antennas, and more particularlyto distinguishing signals transmitted in a MIMO timeslot from multipleantennas.

2. Description of the Related Art

Bursts belonging to a Time Division Multiple Access (TDMA) systemconsists of a training sequence and a guard period in addition to thedata payload. The training sequence may occur at the start of the burst(preamble), middle of the burst (midamble), or end of the burst(postamble). In general there may be multiple training sequences withina single burst. The training sequence used in a mobile radio system istypically a midamble. The guard period is placed at the start and/or endof a burst to reduce interference arising from dispersive channels.

In Code Division Multiple Access (CDMA) systems, multiple bursts may betransmitted simultaneously over a Time Slot (TS), each spread by adistinct signature sequence or channelization code. In a TimeDivision-Code Division Multiple Access (TD-CDMA) system, such as UTRATDD, a mapping between a channelization code and a midamble is definedsuch that the channelization code of a burst may be derived implicitlyusing its midamble sequence.

However, although training sequences may facilitate reception, the useof training sequences tends to be suboptimal in many communicationsystems. Particularly, in MIMO systems a suboptimal performance tends tobe achieved.

Hence, an improved system for generating signals in a MIMO timeslotwould be advantageous and in particular a system allowing increasedflexibility, reduced complexity and/or improved performance would beadvant.

SUMMARY OF THE INVENTION

Accordingly, the invention seeks to mitigate, alleviate or eliminate oneor more of the abovementioned disadvantages singly or in anycombination.

An accordance with a first aspect of the invention, there is provided amethod of generating signals in a MIMO timeslot, the method comprising:selecting a first training sequence; preparing a first data payload;generating a first signal including the prepared first data payload andthe first training sequence; transmitting the first signal in a MIMOtimeslot from a first antenna of a network element; selecting a secondtraining sequence, wherein the second training sequence is differentfrom first training sequence; preparing a second data payload;generating a second signal including the prepared second data payloadand the second training sequence; and transmitting the second signal inthe MIMO timeslot from a second antenna of the network element.

Some embodiments of the invention provide a method to uniquely identifywhich of multiple base station antennas transmits a timeslot burst ofdata.

Some embodiments of the present invention provide a non-overlapping setof midambles that are allocated to bursts transmitted from eachtransmitter antenna element. Thus, midambles used on one antenna are notused on other antennas of the base station.

Some embodiments of the present invention provide a common midamblesequence is allocation for all bursts transmitted from a transmitterantenna element simultaneously. While other embodiments of the presentinvention provide a distinct midamble allocation for each bursttransmitted simultaneously.

Some embodiments of the present invention provide a midamble sequenceallocation that is fixed for each transmitter antenna element.

Some embodiments of the present invention allow the number of burststransmitted from each transmitter antenna to be either partially (i.e.with ambiguity) or fully (i.e. without ambiguity) derived from themidamble sequences allocated to the bursts.

Some embodiments of the present invention provide a set of distinctmidamble sequences allocated to bursts transmitted simultaneously thatare chosen such that MIMO channels can be estimated accurately andefficiently.

Some embodiments of the present invention provide a method of midambleallocation is applied to a UTRA TDD system.

Some embodiments of the present invention further provide a fortransmitting a first indication of an association between the selectedfirst training sequence and the first antenna.

Some embodiments of the present invention further provide a fortransmitting a second indication of an association between the selectedsecond training sequence and the second antenna.

Some embodiments of the present invention further provide wherein thetransmitting the indication includes signalling the indication in acontrol channel message.

Some embodiments of the present invention further provide a forselecting a third training sequence, wherein the third training sequenceis different from second training sequence; and preparing a third datapayload; wherein the generating of the first signal further includes theprepared third data payload and the third training sequence.

Some embodiments of the present invention further provide a forpreparing a fourth data payload; wherein the generating of the secondsignal further includes the prepared fourth data payload and the thirdtraining sequence.

Some embodiments of the present invention further provide wherein theselecting of the first training sequence includes selecting of the firsttraining sequence based on a total number of data payloads included inthe first signal.

Some embodiments of the present invention further provide wherein theselecting of the second training sequence includes selecting of thesecond training sequence based on a total number of data payloadsincluded in the second signal.

Some embodiments of the present invention further provide for selectinga first channelization code for the first data payload; wherein thepreparing a first data payload includes applying the selected firstchannelization code; and wherein the selecting of the first trainingsequence includes selecting of the first training sequence based on theselected first channelization code.

Some embodiments of the present invention further provide fordetermining a burst type; wherein the selecting of the first trainingsequence is based on the determined burst type.

Some embodiments of the present invention further provide wherein theselecting of the first training sequence is based on a total number oftransmit antennas NT.

Some embodiments of the present invention further provide wherein thefirst training sequence is a midamble sequence.

Some embodiments of the present invention further provide wherein thefirst training sequence is a preamble sequence.

Some embodiments of the present invention further provide wherein thefirst training sequence is a post-amble sequence.

Some embodiments of the present invention further provide wherein thenetwork element is a base station.

Some embodiments of the present invention further provide wherein thenetwork element is a mobile terminal.

Some embodiments of the present invention further provide wherein: thepreparing of the first data payload includes: channelizing the firstdata payload with a channelization code; and puncturing the channelizedfirst data payload with a first punching scheme; the preparing of thesecond data payload includes: channelizing the second data payload withthe channelization code; and puncturing the channelized second datapayload with a second punching scheme, wherein the second punchingscheme differs from the first punching scheme; and the second datapayload is the same as the first data payload.

Some embodiments of the present invention further provide wherein: theselecting of the first training sequence includes selecting a firstplurality of training sequences; the preparing of the first data payloadincludes preparing a first plurality of data payloads; the generatingthe first signal includes generating the first signal including theprepared first plurality of data payload and the first plurality oftraining sequences; the selecting of the second training sequenceincludes selecting a second plurality of training sequences, whereineach of the selected training sequences in the second plurality oftraining sequences is different from each of the selected trainingsequences in the first plurality of training sequences; the preparingthe second data payload includes preparing a second plurality of datapayloads; and the generating the second signal includes generating thesecond signal including the prepared second plurality of data payloadsand the second plurality of training sequences.

According to a second aspect of the invention, there is provided amethod of processing signals in a MIMO timeslot, wherein the MIMOtimeslot includes a first burst from a first transmit antenna and asecond burst from a second transmit antenna, wherein the first andsecond bursts each contain one or more data payloads each encoded with arespective code, and wherein each payload corresponds to a midamble, themethod comprising: receiving a signal in the MIMO timeslot; detecting afirst midamble in the signal; extracting out a first payload transmittedfrom the first transmit antenna of a network element based on thedetected first midamble; detecting a second midamble in the signal,wherein the second midamble is different from the first midamble; andextracting out a second payload transmitted from the second transmitantenna of the network element based on the detected second midamble.

Some embodiments of the present invention further provide for:characterizing a first channel formed between the first transmit antennaand the receiver using the detected first midamble; and extracting out athird payload transmitted from the first transmit antenna.

Some embodiments of the present invention provide a method of selectingtraining sequence for a burst, the method comprising: determining anumber of transmit antennas of a base station; determining an antennafrom the number of transmit antennas to transmit the burst; determininga training sequence length; and selecting a training sequence based onthe determined number of transmit antennas, the determined antenna andthe determined training sequence length.

Some embodiments of the present invention provide a method of selectingtraining sequence for a burst, the method comprising: determining anumber of transmit antennas of a base station; determining an antennafrom the number of transmit antennas to transmit the burst; determininga number of payloads to be transmitted in a MIMO timeslot from thedetermined antenna; and selecting a training sequence based on thedetermined number of transmit antennas, the determined antenna and thedetermined number of payloads.

Some embodiments of the present invention provide a method of selectingtraining sequence for a burst, the method comprising: determining anumber of transmit antennas of a base station; determining an antennafrom the number of transmit antennas to transmit the burst; determininga code to encode a payload; and selecting a training sequence based onthe determined number of transmit antennas, the determined antenna andthe determined code.

According to a third aspect of the invention, there is provided anapparatus for generating signals in a MIMO timeslot, the apparatuscomprising: means for selecting a first training sequence; means forpreparing a first data payload; means for generating a first signalincluding the prepared first data payload and the first trainingsequence; means for transmitting the first signal in a MIMO timeslotfrom a first antenna of a network element; means for selecting a secondtraining sequence, wherein the second training sequence is differentfrom first training sequence; means for preparing a second data payload;means for generating a second signal including the prepared second datapayload and the second training sequence; and means for transmitting thesecond signal in the MIMO timeslot from a second antenna of the networkelement.

It will be appreciated that the optional features, comments and/oradvantages described above with reference to the method for generatingsignals apply equally well to the apparatus for generating signals andthat the optional features may be included in the apparatus forgenerating signals individually or in any combination.

Other features and aspects of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings which illustrate, by way of example, the featuresin accordance with embodiments of the invention. The summary is notintended to limit the scope of the invention, which is defined solely bythe claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the drawings, in which:

FIG. 1 shows an example of a MIMO system including a base station withtwo transmit antennas and a mobile terminal with two receive antennas.

FIG. 2 illustrates a transmission of a disjoint set of midamblesequences, in accordance with the present invention.

FIG. 3 illustrates a transmission of fixed midambles, in accordance withthe present invention.

FIG. 4 illustrates a transmission of a common midamble, in accordancewith the present invention.

FIG. 5 illustrates a transmission of a default midamble, in accordancewith the present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which illustrate several embodiments of the present invention.It is understood that other embodiments may be utilized and mechanical,compositional, structural, electrical, and operational changes may bemade without departing from the spirit and scope of the presentdisclosure. The following detailed description is not to be taken in alimiting sense, and the scope of the embodiments of the presentinvention is defined only by the claims of the issued patent.

Some portions of the detailed description which follows are presented interms of procedures, steps, logic blocks, processing, and other symbolicrepresentations of operations on data bits that can be performed oncomputer memory. A procedure, computer executed step, logic block,process, etc., are here conceived to be a self-consistent sequence ofsteps or instructions leading to a desired result. The steps are thoseutilizing physical manipulations of physical quantities. Thesequantities can take the form of electrical, magnetic, or radio signalscapable of being stored, transferred, combined, compared, and otherwisemanipulated in a computer system. These signals may be referred to attimes as bits, values, elements, symbols, characters, terms, numbers, orthe like. Each step may be performed by hardware, software, firmware, orcombinations thereof.

Several embodiments of the invention are described below. Theseembodiments are described with reference to 3GPP UTRA TDD systems,specifications and recommendations, but are applicable more generally.

A midamble is a sequence having special numeric properties, which areeither known to or may be derived by a receiver. A receiver may be ableto estimate a channel that a burst passes through using its knowledge ofwhat was transmitted as the training sequence segment of the burst. Thedata payload may be detected and demodulated reliably based on theknowledge of the channel. Thought concepts described herein aredescribed with reference to midambles, a training sequence placed atother locations of a burst are also applicable. For example, thetraining sequence may be placed at the beginning of the burst (preamble)or at the end of the burst (post-amble). Apart from its primary purposeof enabling channel estimation, a training sequence, such as a midamble,may also be used to carry information that assists a receiver indetecting and demodulating data payload.

A CDMA-receiver may provide improved performance when it has knowledgeof active channelization codes used in a burst. For example, in UTRATDD, the receiver is able to implement Multi-User Detection (MUD) with alist of active channelization codes derived from midambles detected in atimeslot.

Multiple-Input-Multiple-Output (MIMO) transmissions schemes employmultiple antenna elements at a transmitter and at a receiver to improvespectral efficiency. The receiver estimates each channel between eachtransmitter-receiver antenna element pair. A channel in a system with atransmitter having multiple transmit antennas and a receiver havingmultiple receive antennas may be referred to as a MIMO channel.

Each burst is transmitted from a single transmit antenna of atransmitter having multiple transmit antennas. Antenna elements arephysically spaced such that the MIMO channels are sufficientlyuncorrelated. For example, transmit antennas may be spaced by at leastone-half of a wavelength. An example of a MIMO system may be a systemconsisting of a single base station having two transmit antennas and amobile terminal that has two receive antennas.

FIG. 1 shows a single base station 100 that has two antennas labeledantenna NB₁ and antenna NB₂ and a mobile terminal 110 that has twoantennas labeled antenna UE₁ and antenna UE₂. This transmitter-receiversystem has four MIMO channels. Channel 1-1 exists between antenna NB₁and antenna UE₁. Channel 1-2 exists between antenna NB₁ and antenna UE₂.Channel 2-1 exists between antenna NB₂ and antenna UE₁. Channel 2-2exists between antenna NB₂ and antenna UE₂.

In general, an actual MIMO system includes multiple base stationsservicing a number of mobile terminals. Therefore, multiple MIMOchannels will exist among antenna elements of these multiple networkelements.

Introducing diversity, utilizing spatial multiplexing or through acombination of both diversity and spatial multiplexing may improvespectral efficiency in a MIMO system. Diversity gain may be obtainedwhen two or more bursts carrying the same information are transmittedfrom different transmitter antenna elements; a receiver may be able tocombine replicas of the same information that have passed throughdifferent channels.

On the other hand, by taking advantage of spatial multiplexing, it mayalso be possible in a MIMO system to reliably detect up to min(N_(T),N_(R)) bursts spread with a common channelization code transmitted ondistinct antenna elements, where N_(T) and N_(R) denote a number oftransmit and receive antennas respectively. Through the use of MIMOtransmissions, it may be possible to transmit multiple bursts having acommon channelization code where each burst is transmitted from adifferent transmit antenna.

For example, in FIG. 1, a base station 100 may transmit a burstcontaining payload data X using channelization code n from antenna NB₁,which is received by antennas UE₁ and UE₂. Base station 100 maysimultaneously transmit a burst containing data Y using the samechannelization code n from antenna NB₂, which is received by antennasUE₁ and UE₂. Furthermore, a mobile terminal 110 may decode bothtransmissions from antennas NB₁ and NB₂ and decode both data X and dataY.

Alternatively, a MIMO system may transmit different versions of the samedata X from antennas NB₁ and NB₂. For example, if data X isconvolutionally coded and then punctured, antennas NB₁ and NB₂ maytransmit differently punctured versions X₁ and X₂ of the data X.Consequently, a transmitter and a receiver may communicate up tomin(N_(T), N_(R)) times more bursts within a MIMO timeslot as comparedto a single-antenna (non-MIMO) transmitter-receiver pair.

In existing non-MIMO systems, such as Release 5 UTRA TDD, a maximumnumber of midambles that can be transmitted in a timeslot is equal to amaximum number of channelization codes that are to be transmitted in thetimeslot. This allows a channel estimate to be derived at the receiverfor each channelization code.

For example, there are several midamble allocation schemes that exist inUTRA TDD mode as defined in the 3^(rd) Generation Partnership Project(3GPP) document 3GPP TS 25.221 titled “Physical channels and mapping oftransport channels onto physical channels (TDD)”, hereinafter 3GPP TS25.221. Midamble allocation schemes are also described in correspondingpatent application filed on May 4, 2004, (U.S. patent application Ser.No. 10/838,983) and titled “Signalling MIMO Allocations”, which isincorporated herein by reference.

Some midamble allocation schemes provide a one-to-one relationshipbetween bursts in a timeslot and their corresponding channelizationcodes. A mapping of a midamble sequence to a burst may be done through amapping of burst channelization codes. That is, each midamble sequenceis paired with a single channelization code. Similarly, eachchannelization code is paired with a single midamble sequence.

This one-to-one midamble allocation scheme is not applicable for generalMIMO transmissions where a common channelization code is used in two ormore bursts in a MEMO timeslot. Known schemes require a channelizationcode to be assigned a distinct midamble sequence such that a receiver isable to estimate the MIMO channel.

In FIG. 1, a MIMO receiver (mobile terminal 110) needs to be able toderive the MIMO channel for channelization code n at antenna UE₁ forboth Channel 1-1 and Channel 2-1. Estimates for these two channelscannot be derived from a single midamble sequence. That is, if bothbursts include the same midamble, a MIMO receiver is unable todistinguish the bursts and estimate the channels.

A common midamble allocation scheme applied to a single channel(non-MIMO) system allows a single midamble sequence to be is transmittedfor all bursts from a base station antenna to a mobile terminal antenna.The mobile terminal is able to derive a channel estimate for the singlechannel. This common midamble allocation scheme is not applicable toMIMO systems since a single receiver antenna will be unable to derivechannel estimates for channels created by multiple transmit antennas.Hence, a new midamble allocation scheme is desired for MIMO transmissionsystems.

In some embodiments of the invention, bursts may be allocated a midamblesequence such that a receiver may be able to estimate a channel formedbetween a transmitter-receiver antenna pair in a MIMO system. In someembodiments of the present invention, at least one burst transmittedfrom each transmit antenna is allocated a midamble sequence that is notallocated to bursts transmitted from other antenna elements.

FIG. 2 illustrates a transmission of a disjoint set of midamblesequences, in accordance with the present invention. A base station 200has two transmit antennas: antenna NB₁ and antenna NB₂. Base station 200transmits midambles M₁ and M₂ from antenna NB₁. Base station 200 alsotransmits midambles M₂ and M₃ from antenna NB₂. Midamble M₁ is nottransmitted from antenna NB₂ but is transmitted from antenna NB₁.Similarly, midamble M₃ is not transmitted from antenna NB₁ but istransmitted from antenna NB₂. Whereas, midamble M₂ is transmitted fromboth antenna NB₁ and antenna NB₂.

According to some embodiments, midamble codes may be reused in a MIMOtimeslot on different antennas. If a transmitter transmits a firstsignal from a first antenna NB₁ with midambles M₁ and M₂ (as shown inFIG. 2) and a second signal from a second antenna NB₂ with midambles M₃and M₂, midamble M₂ is reused. A receiver may use a channelcharacterized by midamble M₁ to retrieve payload data associated withboth midambles M₁ and M₂ from the first antenna NB₁. Similarly, thereceiver may use a channel characterized by midamble M₃ to retrievepayload data associated with both midambles M₃ and M₂ from the secondantenna NB₂.

In some embodiments of the invention, a mapping of midambles totransmitter antenna elements is signaled implicitly or explicitly to thereceiver. For example, a receiver may derive a mapping implicitlythrough the combination of distinct midambles it detects simultaneously.Alternatively, a mapping may be signaled to the receiver explicitlythrough control channels.

In some embodiments of the invention, a receiver estimates MIMO channelscorresponding to each transmit-receive antenna pair. A receiver mayconsider all distinct midamble sequences transmitted simultaneously.

A unique midamble sequence is allocated to a set of bursts of a timeslottransmitted from a transmit antenna. That is, a midamble sequencem^([i]) allocated to a set of bursts transmitted simultaneously from ani-th transmitter antenna element is chosen from a set of midamblesequences M_(i) such that the sets M₁, M₂ . . . M_(N) _(T) arenon-overlapping. In these embodiments, no midamble sequence in set M_(i)is equal to a midamble in set M_(j) for i≠j.

In some embodiments of the invention, a fixed midamble sequence m^([i])is assigned to all bursts transmitted from a transmit antenna during atimeslot. For example, a midamble sequence defined in 3GPP TS 25.221with K_(Cell)=6 and Burst type=2 and K_(Cell)=4, 8 or 16 with Bursttypes=1 and 3 may be allocated as given in TABLE 1 where N_(T)represents a number of transmit antennas. The midamble shifts areenumerated as per Clause 5A.2.3 of 3GPP TS 25.212.

TABLE 1 and FIG. 3 show a first midamble allocation scheme. A midambleis selected based on a total number of transmit antennas (N_(T)) andbased on which antenna the burst, containing the midamble, will betransmitted. The i-th antenna element uses the midamble sequencem^([i]), which may be selected from a group of midamble sequencesm^((k)), where k is an index to the possible midamble sequences.

TABLE 1 Example of Fixed Midamble Allocation for MIMO TransmissionsBurst types Total Burst Type 2 Burst Type 1 and 3 number of L_(m) = 256,K_(cell) = 6 L_(m) = 512, K_(cell) = 4, 8, 16 Antenna m^([i]): k-thmidamble m^((k)) is assigned m^([i]): k-th midamble m^((k)) is assignedto Elements bursts from antenna element i, where i = 1 burst fromantenna element i, where i = 1 N_(T) to N_(T) to N_(T) 2 m^([1]) = m⁽¹⁾m^([2]) = m⁽³⁾ m^([1]) = m⁽¹⁾ m^([2]) = m⁽⁵⁾ 4 m^([1]) = m⁽¹⁾ m^([2]) =m⁽³⁾ m^([3]) = m⁽²⁾ m^([4]) = m⁽⁴⁾ m^([1]) = m⁽¹⁾ m^([2]) = m⁽⁵⁾ m^([3])= m⁽³⁾ m^([4]) = m⁽⁷⁾

A Burst Type=2 has a training sequence that is 256 chips long (L_(m)) ina UTRA TDD system. K_(Cell) identifies which group of a midamble asequence is selected. For example, K_(Cell)=6 means there are sixmidambles in the group.

Some embodiments of the present invention use a fixed allocation ofmidambles where each transmit antenna element of a transmitter isassigned a different midamble.

FIG. 3 illustrates transmission of fixed midambles in accordance withthe present invention. In the example shown, base station 300 has twoMIMO transmit antennas: antenna NB₁ and antenna NB₂. Additionally,assume that K_(Cell)=6 and Burst type=2. All bursts that are transmittedfrom antenna NB₁ are transmitted with midamble m⁽¹⁾. All bursts that aretransmitted from antenna NB₂ are transmitted with midamble m⁽³⁾.Midambles m⁽¹⁾ and m⁽³⁾ are distinct.

One unique and different midamble may be used in each group a bursttransmitted from multiple antennas in a MIMO timeslot. FIG. 3, forexample, shows a first group of payloads being transmitted with a commonmidamble m⁽¹⁾ on a first antenna NB₁. Each of the payloads may beencoded with a channelization code. A second antenna NB₂ is used totransmit different payloads. The different payloads have a commonmidamble m⁽³⁾ Channelization codes used to encode the payloads on NB₁may all be the same, partially the overlapping or all different than thecodes used to encode the payloads on NB₂.

In some embodiments of the invention, a common midamble sequence m^([i])is allocated to all bursts transmitted from the i-th antenna element andmay be chosen from the set M_(i) based on a number of bursts transmittedfrom the transmit antenna.

A set of bursts transmitted simultaneously from a transmit antenna areallocated a midamble sequence that is determined by the size of the setof data payloads. For a given number of transmit antennas N_(T), afunction ƒ_(N) _(T) (i, n_(i)) maps the transmit antenna index i and anumber of bursts n_(i) transmitted from the i-th antenna element, to amidamble sequence m^([i]) where m^([i]) is defined as m^([i])=ƒ_(N) _(T)(i, n_(i)) such that ƒ_(N) _(T) (i, n_(i))≠ƒ_(N) _(T) , (j, n_(j)) ifi≠j. This ensures that a receiver is able to derive on which transmitantenna a midamble was transmitted without ambiguity. There may be,however, ambiguity in determining a total number of bursts transmittedfrom each transmit antenna. For example, a midamble sequences defined in3GPP TS 25.221 with K_(Cell)=16 with Burst types=1 and 3 may beallocated as given in TABLE 2. The midamble shifts are enumerated as perClause 5A.2.3 in 3GPP TS 25.212.

TABLE 2 and FIG. 4 show a second midamble allocation scheme. A midambleis selected based on a total number of transmit antennas (N_(T)) and anumber of bursts (n_(i)) that the timeslot will carry for a transmitantenna element.

TABLE 2 Example of Common Midamble Allocation for MIMO TransmissionsTotal number of Antenna m^([i]) Elements n_(i): Number of burstsm^([i]): k-th midamble m^((k)) assigned to antenna element N_(T) onantenna element i i, where i = 1 to N_(T) 4 n_(1,2,3,4) = 1, 5, 9 or 13m^([1]) = m⁽¹⁾ m^([2]) = m⁽⁵⁾ m^([3]) = m⁽⁹⁾  m^([4]) = m⁽¹³⁾n_(1,2,3,4) = 2, 6, 10 or 14 m^([1]) = m⁽²⁾ m^([2]) = m⁽⁶⁾ m^([3]) =m⁽¹⁰⁾ m^([4]) = m⁽¹⁴⁾ n_(1,2,3,4) = 3, 7, 11 or 15 m^([1]) = m⁽³⁾m^([2]) = m⁽⁷⁾ m^([3]) = m⁽¹¹⁾ m^([4]) = m⁽¹⁵⁾ n_(1,2,3,4) = 4, 8, 12 or16 m^([1]) = m⁽⁴⁾ m^([2]) = m⁽⁸⁾ m^([3]) = m⁽¹²⁾ m^([4]) = m⁽¹⁶⁾ 2n_(1,2) = 1 or 9 m^([1]) = m⁽¹⁾ m^([2]) = m⁽⁹⁾  n_(1,2) = 2 or 10m^([1]) = m⁽²⁾ m^([2]) = m⁽¹⁰⁾ n_(1,2) = 3 or 11 m^([1]) = m⁽³⁾ m^([2])= m⁽¹¹⁾ n_(1,2) = 4 or 12 m^([1]) = m⁽⁴⁾ m^([2]) = m⁽¹²⁾ n_(1,2) = 5 or13 m^([1]) = m⁽⁵⁾ m^([2]) = m⁽¹³⁾ n_(1,2) = 6 or 14 m^([1]) = m⁽⁶⁾m^([2]) = m⁽¹⁴⁾ n_(1,2) = 7 or 15 m^([1]) = m⁽⁷⁾ m^([2]) = m⁽¹⁵⁾ n_(1,2)= 8 or 16 m^([1]) = m⁽⁸⁾ m^([2]) = m⁽¹⁶⁾

FIG. 4 illustrates a transmission of a common midamble in accordancewith the present invention. A MIMO base station 400 has two transmitantennas. In the example shown, base station 400 transmits payload datausing two codes from antenna NB₁ and thus applies midamble m⁽²⁾ for atransmission from antenna NB₁ as realized from TABLE 2 above. Basestation 400 also transmits payload data using four codes from antennaNB₂ and thus applies midamble m⁽¹²⁾ for the transmission from antennaNB₂.

When the mobile terminal receives midamble m⁽²⁾, it deduces that eithertwo or ten codes are being transmitted from antenna NB₁. The mobileterminal then performs further signal processing to derive an actualnumber of codes transmitted from antenna NB₁. In this example, furthersignal processing by the mobile terminal should show that two codes weretransmitted.

Similarly, when the mobile terminal receives midamble m⁽¹²⁾, it deducesthat either four or twelve codes are being transmitted from antenna NB₂.The mobile terminal then performs further signal processing to derivethe actual number of codes transmitted from antenna NB₂. In this casefour codes were transmitted. A midamble sequence used to signal a givennumber of codes as active on antenna NB₁ is distinct from any of themidamble sequences that are transmitted from antenna NB₂ and vice versa.

In some embodiments of the invention, a midamble allocated to a burstmay be determined based on its corresponding channelization code and thetransmit antenna from which it is transmitted.

Each burst is allocated a midamble sequence that is determined by whichtransmit antenna transmits the bursts and by its channelization code.For a given number of transmitter antenna elements, an associationbetween a midamble sequence m, and the transmitter antenna element indexi, the channelization code c may be defined through a mapping functionm=g(i, c) such that g(i, c)≠g(j, c′) for i≠j. This ensures that areceiver may unambiguously map midambles to a transmit antenna, however,there may be some ambiguity as to the channelization code used. Forexample, a midamble sequences defined in 3GPP TS 25.221 with K_(Cell)=16and Burst types=1 and 3 may be allocated as given in TABLE 3.

TABLE 3 and FIG. 5 show a third midamble allocation scheme. A midambleis selected based on a total number of transmit antennas (N_(T)), inwhich antenna the burst, containing the midamble, will be transmittedand based on which channelization codes are included with the midamblein the burst. The list of codes is represented by c₁₆ ^((i-th))), whichindicates that the i-th code from a list of codes is selected where thelist contains 16 items.

TABLE 3 Example of Default Midamble Allocation Selected MidambleSequence for an antenna element Antenna Antenna Antenna Antenna element#1 element #2 element #3 element #4 N_(T) Channelization Codes m^([1])m^([2]) m^([3]) m^([4]) 2 c₁₆ ⁽¹⁾ or c₁₆ ⁽²⁾ m⁽¹⁾ m⁽⁹⁾ c₁₆ ⁽³⁾ or c₁₆⁽⁴⁾ m⁽²⁾ m⁽¹⁰⁾ c₁₆ ⁽⁵⁾ or c₁₆ ⁽⁶⁾ m⁽³⁾ m⁽¹¹⁾ c₁₆ ⁽⁷⁾ or c₁₆ ⁽⁸⁾ m⁽⁴⁾m⁽¹²⁾ c₁₆ ⁽⁹⁾ or c₁₆ ⁽¹⁰⁾ m⁽⁵⁾ m⁽¹³⁾ c₁₆ ⁽¹¹⁾ or c₁₆ ⁽¹²⁾ m⁽⁶⁾ m⁽¹⁴⁾ c₁₆⁽¹³⁾ or c₁₆ ⁽¹⁴⁾ m⁽⁷⁾ m⁽¹⁵⁾ c₁₆ ⁽¹⁵⁾ or c₁₆ ⁽¹⁶⁾ m⁽⁸⁾ m⁽¹⁶⁾ 4 c₁₆ ⁽¹⁾,c₁₆ ⁽²⁾, c₁₆ ⁽³⁾ or c₁₆ ⁽⁴⁾ m⁽¹⁾ m⁽⁹⁾ m⁽²⁾ m⁽¹⁰⁾ c₁₆ ⁽⁵⁾, c₁₆ ⁽⁶⁾, c₁₆⁽⁷⁾ or c₁₆ ⁽⁸⁾ m⁽³⁾ m⁽¹¹⁾ m⁽⁴⁾ m⁽¹²⁾ c₁₆ ⁽⁹⁾, c₁₆ ⁽¹⁰⁾, c₁₆ ⁽¹¹⁾ or c₁₆⁽¹²⁾ m⁽⁵⁾ m⁽¹³⁾ m⁽⁶⁾ m⁽¹⁴⁾ c₁₆ ⁽¹³⁾ or c₁₆ ⁽¹⁴⁾, c₁₆ ⁽¹⁵⁾ or c₁₆ ⁽¹⁶⁾m⁽⁷⁾ m⁽¹⁵⁾ m⁽⁸⁾ m⁽¹⁶⁾

FIG. 5 illustrates a transmission of a default midamble in accordancewith the present invention. A MIMO base station 500 has two transmitantennas. In the example shown, base station 500 transmits codes c₁₆ ⁽³⁾and c₁₆ ⁽⁴⁾ from antenna NB₁ and thus applies midamble m⁽²⁾ for thetransmission from antenna NB₁ as may be realized from TABLE 3 above.Base station 500 also transmits codes c₁₆ ⁽¹⁾ and c₁₆ ⁽⁶⁾ from antennaNB₂ and thus base station 500 applies midambles m⁽⁹⁾ and m⁽¹¹⁾ for theburst associated to c₁₆ ⁽¹⁾ and c₁₆ ⁽⁶⁾, respectively.

When a mobile terminal receives midamble m⁽²⁾, it deduces that eitherc₁₆ ⁽³⁾ or c₁₆ ⁽⁴⁾ or both c₁₆ ⁽³⁾ and c₁₆ ⁽⁴⁾ are being transmittedfrom antenna NB₁. Similarly, when the mobile terminal receives midamblem⁽⁹⁾, it deduces that either c₁₆ ⁽¹⁾ or c₁₆ ⁽²⁾ or both c₁₆ ⁽¹⁾ and c₁₆⁽²⁾ are being transmitted from antenna NB₂. Furthermore, when the mobileterminal receives midamble m⁽¹¹⁾, it deduces that either c₁₆ ⁽⁵⁾ or c₁₆⁽⁶⁾ or both c₁₆ ⁽⁵⁾ and c₁₆ ⁽⁶⁾ are being transmitted from antenna NB₂.

Some embodiments of the invention allow a receiver to estimate each MIMOchannel between a transmitter-receiver antenna pair. Additionally,higher spectral efficiency of a network air interface is realizedthrough a use of MIMO transmission techniques that achieve diversity,spatial multiplexing or a combination of both; and higher peakthroughput over the network air interface through the use MIMOtransmission techniques that achieve spatial multiplexing. This resultsin increased average throughput, increased number of users and lowertransmission power per user.

Using a fixed or common midamble allocation scheme also allows channelestimation to be performed more accurately as a minimum number ofdistinct midambles is transmitted simultaneously. These schemes alsoreduce interference. Consequently, a performance and capacity of thenetwork are improved further. Furthermore, these schemes may lowercomplexity of a mobile terminal. If bursts transmitted from the sametransmit antenna are allocated a common midamble, the processing andmemory requirements for channel estimation is reduced.

Midamble sequences may be allocated to bursts such that a receiver isable to estimate a channel formed between each transmit-receiver antennapair. At least one burst transmitted from a particular antenna elementmay be allocated a midamble sequence that is not allocated to burststransmitted from other transmitter antenna elements.

Processing prior to using a MUD may be used to determine which codes aretransmitted in a burst or group of bursts in a timeslot or a MIMOtimeslot. Signal processing, such as a matched filter, may be used todetermine which codes are transmitted in a burst. Some methods inheremay be used to narrow down a list of possible codes transmitted.

According to some embodiments, a receiver may combine channel estimatesfrom multiple channel estimates. For example, a receiver may determine achannel estimate based on a first midamble. A second midamble in thesame timeslot from the same antenna may act as interferences during thischannel estimate. Similarly, the receiver may determine a channelestimate based on the second midamble. The receiver may combine theresults to form an improved channel estimate.

Channel estimates may be used to scale received signals from more thanone antenna. A receiver may use a structure that is enhanced when signalpowers are properly scaled. For example, a signal with 16 coded payloadsfrom a first antenna may be scaled to a high amount than a second signalhaving a single coded payload from a second antenna received during thesame MIMO timeslot.

While the invention has been described in terms of particularembodiments and illustrative figures, those of ordinary skill in the artwill recognize that the invention is not limited to the embodiments orfigures described. For example, many of the embodiments described aboverelate to communication on a downlink. Other embodiments are applicableto the uplink. That is, where the mobile terminal has a transmitter withmultiple transmit antenna elements and the base station has a receiverwith multiple receive antenna elements.

The figures provided are merely representational and may not be drawn toscale. Certain proportions thereof may be exaggerated, while others maybe minimized. The figures are intended to illustrate variousimplementations of the invention that can be understood andappropriately carried out by those of ordinary skill in the art.

Therefore, it should be understood that the invention can be practicedwith modification and alteration within the scope of the appendedclaims. The description is not intended to be exhaustive or to limit theinvention to the precise form disclosed. It should be understood thatthe invention can be practiced with modification and alteration and thatthe invention be limited only by the claims.

1. A method of communicating with mobile terminal from a network elementof a mobile radio network, the network element and the mobile terminaleach including a first antenna and a second antenna, the methodcomprising: receiving an indication for a MIMO downlink channel forcommunicating with the mobile terminal; selecting at least one firsttraining sequence from a set of training sequences for allocation to thefirst antenna of the network element; preparing at least one datapayload; generating a first signal including the prepared at least onedata payload and the at least one training sequence; transmitting thefirst signal as a MIMO transmission forming the downlink channel fromthe first antenna of the network element to the mobile terminal; and inresponse to the indication for the MIMO downlink channel forcommunicating with the mobile terminal, selecting at least one secondtraining sequence from the set of training sequences for allocation tothe second antenna of the network element, wherein each of the selectedtraining sequences of the at least one second training sequence isdifferent from each of the selected training sequences of the at leastone first training sequence; preparing at least one second data payload;generating a second signal including the prepared at least one seconddata payload and the at least one second training sequence; transmittingto the mobile terminal the second signal in the downlink MIMO channelfrom the second antenna of the network element simultaneously with thetransmission of the first signal to form the MIMO transmission; and forcorresponding MIMO transmissions in a same position in subsequent framesto that of the MIMO transmission using each of the at least one firsttraining sequence only for transmissions from the first antenna of thenetwork element, and using each of the at least one second trainingsequence only for transmissions from the second antenna of the networkelement.
 2. The method of claim 1, further comprising: selecting a thirdtraining sequence, wherein the third training sequence is different fromthe at least one second training sequence; and preparing a third datapayload; wherein the generating of the first signal further includes theprepared third data payload and the third training sequence.
 3. Themethod of claim 2, further comprising: preparing a fourth data payload;wherein the generating of the second signal further includes theprepared fourth data payload and the third training sequence.
 4. Themethod of claim 1, wherein the selecting of the at least one firsttraining sequence includes selecting of the at least one first trainingsequence based on a total number of data payloads included in the firstsignal.
 5. The method of claim 2, wherein the selecting of the at leastone second training sequence includes selecting of the at least onesecond training sequence based on a total number of data payloadsincluded in the second signal.
 6. The method of claim 1, furthercomprising: selecting a first channelization code for the at least onefirst data payload; wherein the preparing at least one first datapayload includes applying the selected first channelization code; andwherein the selecting of the at least one first training sequenceincludes selecting of the at least one first training sequence based onthe selected first channelization code.
 7. The method of claim 1,further comprising: determining a burst type; wherein the selecting ofthe at least one first training sequence is based on the determinedburst type.
 8. The method of claim 1, wherein the selecting of the atleast one first training sequence is based on a total number of transmitantennas NT.
 9. The method of claim 1, wherein the at least one firsttraining sequence comprises at least one midamble sequence.
 10. Themethod of claim 1, wherein the at least one first training sequencecomprises at least one post-amble sequence.
 11. The method of claim 1,wherein the at least one first training sequence comprises at least onepost-amble sequence.
 12. The method of claim 1, wherein the networkelement is a base station.
 13. The method of claim 1, wherein thenetwork element is another mobile terminal.
 14. The method of claim 1,wherein: the preparing of the at least one first data payload includes:channelizing the at least one first data payload with a channelizationcode; and puncturing the channelized at least one first data payloadwith a first puncturing scheme; the preparing of the at least one seconddata payload includes: channelizing the at least one second data payloadwith the channelization code; and puncturing the channelized at leastone second data payload with a second puncturing scheme, wherein thesecond puncturing scheme differs from the first puncturing scheme; andthe at least one second data payload is the same as the at least onefirst data payload.
 15. The method of claim 1, wherein the at least onefirst and the at least one second training sequences are selectedfurther based on the first antenna and the second antenna, respectively,and a first and second channelization code, respectively.
 16. The methodof claim 1, wherein the at least one first and the at least one secondtraining sequences are selected based on a predetermined trainingsequence allocation scheme.
 17. The method of claim 1, comprisingproviding the mobile terminal with an indication the first trainingsequence and the allocation to the first antenna and an indication ofthe second training sequence and the allocation to the second antenna,in response to an allocation by the network element of the up-linkchannel.
 18. A network element of a mobile radio network forcommunicating with a mobile terminal, the mobile terminal including afirst and a second antenna, the network element comprising: a receiverconfigured to receive an indication for a MIMO downlink channel forcommunicating with the mobile terminal; a first antenna; a secondantenna; and a transmitter operably coupled to the first antenna and thesecond antenna and configured to select at least one first trainingsequence from a set of training sequences for allocation to the firstantenna of the network element; to prepare at least one data payload; togenerate a first signal including the prepared at least one data payloadand the at least one first training sequence; to transmit the firstsignal as a MIMO transmission forming the downlink channel from thefirst antenna of the network element to the mobile terminal; in responseto the indication for the MIMO downlink channel for communicating withthe mobile terminal, to select at least one second training sequencefrom the set of training sequences for allocation to the second antennaof the network element, wherein each of the selected training sequencesof the at least one second training sequence is different from each ofthe selected training sequences of the at least one first trainingsequence; to prepare at least one second data payload; to generate asecond signal including the prepared at least one second data payloadand the at least one second training sequence; and to transmit to themobile terminal the second signal in the downlink channel from thesecond antenna of the network element simultaneously with thetransmission of the first signal to form the MIMO transmission, whereinthe transmitter is further configured for corresponding MIMOtransmissions in a same position in subsequent frames to that of theMIMO transmission to use each of the at least one first trainingsequence only for the transmissions from the first antenna and each ofthe at least one second training sequence only for transmissions fromthe second antenna.
 19. The network element of claim 18, wherein thetransmitter comprises a base-station transmitter.
 20. The networkelement of claim 18, wherein the transmitter is configured to providethe mobile terminal with a first indication of the selected firsttraining sequence and the allocation to the first antenna and theselected second training sequence and the allocation to the secondantenna in response to an allocation by the network element of theup-link channel.